The semiconductor integrated circuit (IC) industry has experienced rapid growth. Technological advances in IC materials and design have produced generations of ICs where each generation has smaller and more complex circuits than the previous generation. However, these advances have increased the complexity of processing and manufacturing ICs and, for these advances to be realized, similar developments in IC processing and manufacturing are needed. In the course of integrated circuit evolution, functional density (i.e., the number of interconnected devices per chip area) has generally increased while geometry size (i.e., the smallest component (or line) that can be created using a fabrication process) has decreased.
To facilitate the semiconductor device scaling down process, metal gate electrodes may be used instead of conventional polysilicon electrodes. The formation of the metal gate electrodes may involve a gate replacement process, in which a dummy gate electrode is removed to form an opening in its place, and the opening is subsequently filled by metal materials to form the metal gate electrode. However, conventional gate replacement processes may leave an overhang in the opening, which may impede the filling of the opening by the metal material. As such, voids may form in the metal gate, which degrades semiconductor device performance.
Therefore, while existing gate replacement processes have been generally adequate for their intended purposes, they have not been entirely satisfactory in every aspect.